The thing you will need is a pushrod tranny case and mainshaft. All the gears are the same. Then you'll need all the clutch parts to go with it. It's an expensive job unless you have the pieces already. ERC

Thank you. Next question - is there a way to tell from the outside what kind of clutch is in the gear box? Have another Trailblazer with later motor, SMP 4xxx versus SM 2xxx and am wondering if it might have the pushrod (better?) clutch. Owner of scissor type said someone who own several of these said the clutch is a common problem. Read that the scissor was used only for a year or two then changed. Others have suggested later model is a better bet because of parts availability. Your posts indicate you must know a lot about these,any thoughts? Please and thank you. Also, I see these bikes do not appear to have a very high collector value, any insight to why?

On the scissor one the clutch cable goes into the primary. On the pushrod one it goes into the transmission on the back of it. Don't know why they aren't worth more. I just like them. If you end up with the scissor type Hitchcocks has parts new and used for them. ERC

The early Trailblazers from 55 to 57 had the push rod clutch set up. In late 57 they changed over to the scissors or ball ramp type. The 500 twins and Constellation used this clutch too but they switched back by the end of 1960 due to to transmission problems that wouldn't go away due to the ton weighing clutch hanging out on the end of the mainshaft. The AM series gearboxes used on the Apache and Chief models of 1959 were beefed up in a lot of ways but not in th mainshaft or it's support bearings so the problems remained with them until production ended.

Thank you for the insight. Other things equal, would you go for an earlier model SM2700 series engine with push rod clutch know to have stripped spring retainer screw/plate or a later SMP 4100 series with scissor clutch, condition not yet known? Either has certain advantages with respect to other parts needed but both are complete. I see the complete clutch assemblies and parts are available from Hitchcock but not for the scissor model.

The later the engine the more reliable they are. Royal Enfield was excelllent at solving problems when they started to arize. The 58 or later models are the better of the lot as long as they are properly serviced.